Control systems for commercial refrigeration systems generally control cooling capacity in response to variations in refrigeration load. Often this involves on/off control of fixed speed compressors and/or variable control of variable speed compressors. When multiple compressors in a parallel arrangement are used to provide refrigerant to multiple evaporators operating at varying temperatures, suction pressure is generally used as a control variable input to the control system. Often a controller, implementing a proportional-integral-derivative control algorithm, processes a sensed suction pressure common to all the compressors in the parallel arrangement and determines a control output for one or more compressors to maintain cooling capacity at a level that closely matches the refrigeration load presented by the evaporators.